The invention relates to a method and to an apparatus for determining and indicating the quantity of a stored liquid or solid material contained in a container sealable with respect to the atmosphere or any other reference pressure, together with an air, gas or vapor quantity filling the residual volume of the container interior, according to the preamble of claim 1.
Methods and apparatuses for measuring the quantity of a stored liquid or solid material in a container sealable with respect to the atmosphere or some other reference pressure in an intermittent manner by determining the volume or quantity of the gaseous container content by displacing the volume or the quantity of said content using Boyle's law are known in many different forms.
Thus, for example, in known constructions the increase and decrease of the container gas zone volume or the increase and decrease of the gas quantity in the container by means of a cylinder with piston and piston rod connected to the container gas zone by means of a connecting line with a pressure gauge. A pressure compensating device is provided between the cylinder chamber and the atmosphere in such a way that when the piston is extended to the maximum extent a connection is formed between the cylinder chamber and the atmosphere, so that pressure compensation is brought about between the container gas zone and the atmosphere. By inserting the piston in the cylinder the pressure compensating opening is separated from the container and consequently the container gas zone is sealed relative to the atmosphere. By reducing the gas-filled cylinder volume connected to the container gas zone, a further insertion of the piston leads to a pressure rise in the container interior. As this pressure rise is solely dependent on the size of the gas-filled zone and the gas quantity forced in through the piston, the pressure rise gives the volume of the container gas zone and therefore, when the total container volume is known, the stored product quantity filled into the container (German Pat. No. 897 331 and U.S. Pat. No. 1,508,969).
In the case of the aforementioned construction (German Pat. No. 897 331) and similarly acting construction forms and methods, the disadvantage arises that complicated, large-area or volume constructions are required, e.g. cylinder arrangements, additional containers and the like, in order to permanently obtain adequate accuracy of measurement by the principle of measuring the stored product quantity by determining the container gas zone volume or the gaseous content quantity. In addition, cylinder-piston systems must have a high degree of sealing on a long term basis to avoid measuring errors. An acceptable solution of this problem in the case of such arrangements can only be achieved with extremely high technical expenditure and effort, such as e.g. by ground cylinder pistons and walls. The use of cylinder and piston systems in aircraft and motor vehicles is very problematical for weight reasons and space deficiencies for the housing thereof, particularly if easily ignitable air-vapor mixture in the case of flammable liquids or toxic stored materials require an extreme sealing level of the cylinder-piston system. In addition, the space requirement with the piston inserted and extended is the same or even greater.
German Pat. No. 697 341 describes another known apparatus for determining the stored material quantity in a container temporarily sealed with respect to the atmosphere by measuring the pressure rise in the container gas zone through the supply of a gaseous measuring pressure medium. This apparatus fundamentally differs from the aforementioned apparatuses only in that the container gas zone is separated by a gas and liquid-tight, balloon-like, elastic envelope from the stored material, so as to ensure that no explosive gas-air mixture can form in said empty zone. The effective volume of this inflatable envelope changes with the quantity of liquid stored. The envelope must at least be sufficiently large that it can fill the complete container interior in the inflated state and with the container empty.
In the case of said apparatus, apart from the disadvantages of the previously described apparatuses, there is also the additional expenditure of having to incorporate or fit an envelope in the container and whose dimensions, particularly internal dimensions must largely correspond to the container shape.